Cycling and ferries are the only mode of transport in the sparsely populated islands on Sweden's west coast. Photograph: /Rebecca Nicholson

If there is one lesson to learn from a trip up the Bohuslän coastline, it is this: upon accepting an invitation to spend the evening drinking with a Swedish fisherman called Johan, realise that much of the following day will be spent with head in hands, wondering at which point during the singsong, exactly, it became a good idea to get in yet another round.

I have visited Stockholm many times – it’s beautiful to look at, expensive and glamorous – but this time I was touching down instead in Sweden’s more down-to-earth western city, Gothenburg, and heading out to explore Bohuslän, a small coastal province in Götaland, home to the tiny Koster islands. The 170km of coast stretching north towards Strömstad are reputed to match the Norwegian coastline for wild and unpopulated natural beauty.

We arrived in Gothenburg on a sticky summer evening and wandered the picturesque canal, with its cute bridges and majestic Gustav Adolf square (named after the founding father of Sweden). We stopped for cold beers alfresco before spending the night at our floating hotel – the Ibis, housed in a ship on the Gothia river.

The next day, a four-hour train ride took us to Strömstad, the views making the languorous journey a treat: tiny, toybox towns, thousands of rocky, uninhabited islands jutting out of the sea, the train weaving in and out of deep green forests. Strömstad, at the end of the line, is a Disney-pretty seaside resort from which a regular ferry to Koster departs.

There are no cars on its two tiny inhabited islands, Nord and Syd – it’s bicycles only or, if you need some heavy lifting, motorbikes with trailers. The boat was packed with Swedish families showing off spectacularly efficient systems for transporting huge amounts of camping gear on foot.

A short walk from Vettnet dock is the Reservatet Nordkoster, a gorgeous, rustic campsite in the north-east, where you can pitch a tent in the vast forest or on the beach. It wears its eco-credentials with pride: I made the mistake of asking where the showers were, and the woman behind the counter laughed and pointed to the sea. At just four square kilometres, north Koster is smaller than its southern sibling, sparsely inhabited and almost entirely given over to its nature reserve, with a quiet bar/cafe at the Västra Bryggan dock as its social hub. But a stay here is about escape – swim in the sea, cycle across the island, cook fish on a campfire and pretend the rest of the world doesn’t exist.

Johan took us on his boat for the afternoon, where we caught mackerel and hauled up crab pots. Photograph: Rebecca Nicholson

After two blissful days of lazy living, we caught the ferry over to the more populated, bigger south island. The bulk of its visitors appear to be rich Norwegians who moor their yachts just off the coast, but the grand wooden – and rather pricey – Hotel Koster in Ekenäs is a 10-minute cycle from the harbour. A bike is essential here, and a short cycle in any direction uncovers a new adventure.

There are tiny beaches down tracks off most of the coastal roads, upon which you are unlikely to encounter any other people. A track through a gloomy-looking forest emerged on to a crop of rocks from which families were diving into the sea. We borrowed kayaks from a local family and set about trying to negotiate some of the more sheltered outcrops of the archipelago, though this mostly involved being washed up on a rocky beach repeatedly (it’s still the North Sea and those winds are strong). Kosters Trädgårdar, an idyllic cafe and farm, serves delicious produce grown in accordance with the owners’ permaculture principles.

On our last night at Hotel Koster, the bandstand outside was hosting one of the many musical acts that come to stay. This is where we met Johan. Earlier that day, Johan had taken us on his boat for the afternoon, where we caught mackerel and hauled up crab pots full of creatures so huge and mean-looking they deserve their own monster movie. Upon returning to shore we stopped off at the fishmonger’s on the harbour, where we swapped live crab for cooked.

It felt apt to celebrate the catch, so we did, cracking claws and shells open, squeezing nothing but lemon on them, and toasting our success with wine. And then more wine. And the celebrations continued that night as the band began to play. People started to sing. Someone suggested shots.

There, the evening blurs, but I suspect it was brilliant – removed from the sophistication of the city, but refreshing, relaxed and fun.

• Flights were provided by SAS (flysas.com), which flies direct from Heathrow to Gothenburg from about £100 return. Ibis Gothenburg (ibis-goteborg-city.com) has doubles from £65 B&B. Hotel Koster (hotelkoster.se) has doubles from £85 B&B. A pitch at Reservatet Nordkoster (reservatet.nu) costs £13 per night, plus £2 per person per night. To camp in Scandinavia, you need a Camping Card Scandinavia, which costs roughly €16, lasts a year and is available from most campsites